One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, which works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate micro-actuators are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803; U.S. Pat. Nos. 6,671,131 and 6,700,749; and U.S. Publication No. 2003/0168935, the contents of each of which are incorporated herein by reference.
FIGS. 1 and 2 illustrate a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a micro-actuator 105 with a slider 103. The slider 103 has a read/write head (not shown) incorporated therein for reading or writing digital information to the disk 101. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head of the slider 103 to read data from or write data to the disk 101.
Because of the inherent tolerances (e.g. dynamic play) of the VCM and the head suspension assembly, the slider cannot achieve quick and fine position control which adversely impacts the ability of the read/write head 103 to accurately read data from and write data to the disk when only a servo motor system is used. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head 103. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and/or head suspension assembly. The micro-actuator 105 enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
FIGS. 3a-3c illustrate the HGA 100 incorporating a dual-stage actuator in the conventional disk drive device of FIGS. 1 and 2. The slider 103 is partially mounted on a slider support 121. A bump 127 is formed on the slider support 121 to support the center of the slider's back surface. A flex cable 122 with a plurality of traces couples the slider support 121 and a metal base flexure 123.
A suspension load beam 124 with a dimple 125 supports the slider support 121 and flexure 123. The dimple 125 of the suspension load beam 124 supports the bump 127 of the slider support 121. This ensures that the load force from the load beam 124 is applied to the slider center when the head is flying over the disk. A micro-actuator 10 comprising two thin-film PZT pieces is attached on a tongue region 128 and at least partially under the slider 103.
When a voltage is input to the thin-film PZT pieces, one of the two PZT pieces may contract (for example, contract along direction D shown in FIG. 3b), and the other one may expand (for example, expand along direction E shown in FIG. 3b). These contractions and/or expansions enable the slider 103 to rotate around the dimple 125 of the load beam 124 (e.g., rotate along direction C of FIG. 3b), thereby realizing fine displacement of the slider 103.
However, this conventional HGA design inherently possesses some disadvantages. More specifically, as shown in figures, the slider 103 has a trailing edge 134 on which the read/write head is formed and a leading edge 132 opposite to the trailing edge 132. It is clear from the figures that a portion approximately from the center of the slider 103 to the trailing edge 134 (referred to as trailing edge portion) is mainly supported by the slider support 121, while a portion from the center of the slider 103 to the leading edge 132 (referred to as leading edge portion) is approximately supported by nothing.
Since the slider support 121 is usually made of stainless steel and has a large thickness (for example about 18-25 um), a weight of the HGA 100 at trailing edge portion (totality of mass of the slider support 121 and half mass of the slider 103) is larger than weight at leading edge portion (only half mass of the slider 103). In other words, unbalance in weight of the HGA 100 occurs between the trailing edge portion and leading edge portion. Because the slider support 121 with the slider 103 mounted thereon is supported only by the dimple 125, and because weight-unbalance occurs between the leading edge portion and the trailing edge portion, the slider 103 and the slider support 121 will get to be tilt relative to the load beam 124 of the HGA 100. Unfortunately, this undesirable tilting will generate a reaction force which will be directly applied to the load beam 124 through the dimple 125. The frequently occurring reaction forces will induce frequent vibration of the load beam as to degrade resonance characteristics of the entire HGA, thereby further limit the servo bandwidth improvement and TPI improvement of the HGA.
Moreover, this undesirable tilting of the slider increases not only possibility of physical contact friction between the slider and the disk, but also possibility of contamination of the slider ABS when the slider is flying over or landing on the disk.
In addition, this slider tilting will result in big slider flying attitude sensitivity. Namely, the flying attitude of the slider will be easily changed when the slider is flying over the disk, thus adversely affecting head-disk interface (HDI) reliability of the entire disk drive unit.
Thus, it will be appreciated that there is a need in the art for an improved system that does not suffer from one or more of the above-mentioned drawbacks.